Mass Production 17-18

Comparison with Store-Bought Yo-yo 28-29

1SECTION 1: Introduction The base of our yo-yo is the blue cupped part thathas a hole on one side for the set screw and spacer.Although it might seem simple at first, all of its featureswere carefully designed to improve the function andaesthetic of the yo-yo. First, we inserted a metal shim intothe base part to give the yo-yo a weightier feel while it isbeing used. While testing the functionality of the yo-yo, wereceived numerous compliments on its weight. Otherimportant features include the steps on the inside of thebase’s rim. Each serves a different purpose. The top step iswhere the coffee top and foam sits. We put the step at thisheight such that the rounded edge of the coffee top wouldrise slightly above the base. The bottom step seals in themetal shim. The plastic resin molds over the metal, so that once the plastic is cooled, the metalshim cannot be pulled out. The raised platform that molds around the nut also has a function. It isdesigned to be a specific height that will enable it to support the coffee top and foam parts attheir center. This way it is difficult to deform the assembled part by compression. Even thoughthere were many successes in the design of this part, there still is a stub leftover from the gate oneach part. In mass production of these parts, it would be a good idea to put each part throughpost-processing in order to file down the stubs.

The brown coffee top was another successful part.

The smooth surface finish of its cavity mold gives the parta sleek, liquid appearance, making it look similar to coffee.The outer diameter of the coffee top was designed to be, onaverage, ten thousandths larger than the inner diameter ofthe base part for a tight press-fit. As you will see below,the average top actually came out twenty thousandthslarger than the average base. Although we were concernedthat the parts would no longer fit together at first, the press-fit between the two parts turned out to be even better thanbefore. The assembly process might be slightly moredifficult, but the assembled yo-yo is much more robust as aresult. As a result, we are happy with this change. The holes for the white foam in the coffee topwere also a success. Their sizes are only slightly larger than the foam islands that fit throughthem. This helps to make it seem like there really is foam sitting on top of the coffee. The mainissue with this part is that the mill could not fully machine that heart in the top-most island in thecore mold, so there is a small gap between the foam and top at this spot. We would have to usean even smaller endmill to fix this.

2 The coffee foam was successful for many of thesame reasons. It fit well with the coffee top with not mucharea between the foam’s islands and the top’s cavities. Thefoam’s outer diameter stuck out enough such that it couldbe sandwiched between the base and the coffee top. Thislip feature and the base’s raised platform keep the top ofthe foam level with the top of the coffee. One thing wewould change if we had more time to experiment with thethermoforming process would be to see if we can close thespace between the coffee top and foam even more as wellas attempt to make the corners of the foam islands as sharpas possible.

The cup serves as a holder for the yo-yo. Its inner

diameter is large enough that the yo-yo can easily slide inand out of it. We also implemented a step in the cup thatthe yo-yo can sit on, so that the yo-yo does not fall to deepinto the cup. The large base of the cup prevents the cupfrom tipping over due to minor disturbances. We think thequality of the cup could be improved, though. Although weused the thickest sheet available, the rim of the cup is stilltoo flexible. Given the materials, we would use a thickersheet of plastic in order to make the cup more robust.

Overall, our final yo-yo prototype turned out really

well. The assembly is compact and looks good. The metal shims we molded the base around givethe yo-yo a heavier, better feel. The art on the coffee foam fits nicely into the brown coffee top.The tightness of the snap-fit between the coffee top and the base ensures that the yo-yo will stayassembled. Lastly, when the yo-yo is placed in the thermoformed cup, it looks sufficiently likean actual cup of coffee. We are very happy and proud of our finished yo-yo.

3SECTION 2: Part Production AnalysisBase:

4 We were able to produce over 100 base parts. Almost all of the parts were producedwithin the tolerance range of 2.300” + 0.005”, and even those parts that were outside of thisrange could still be used to assemble a complete yo-yo. The standard deviation for the baseproduction run was 0.00195”.

We introduced a disturbance in the process parameters during the production of parts 62

through 72. We decided a good parameter change would be to reduce the cooling time from 20sec to 10 sec. We cannot notice this change in the Shewhart X-bar chart, though. Reducing thecooling time is supposed to increase the shrinkage, but the shim in the base prevented the partfrom shrinking more. The base hardly shrinks as it is, and we already accounted for the lack ofshrinkage in our mold design. As a result, the reduction of cooling time is hardly noticeable.Sadly, this means that we likely could have reduced the cycle time of the base part and optimizedour production run even more, but we were not able to get enough time on the injection moldingmachines to find the minimum acceptable value for every parameter.

We chose our “rational subgroup” size to be four. We chose this number becauseaveraging the dimension of four parts gives a centralized measurement for the inner diameter,and it still leaves us with 28 averaged production runs. Altogether, this gives us a goodrepresentation of the inner diameter dimension the process is producing, as well as give us plentyof data points to put in the Shewhart X-bar graph. The control limits were also set three standarddeviations above and below the measured average. This range was chosen because it enables usto notice outlier average measurements and keep them from making it through production. Threestandard deviations also gives a sufficiently large range to account for the capabilities of theprocesses we use in manufacturing the yo-yo parts. Lastly, it is possible to still assemble our yo-yo using parts with critical dimension measurements within this range, so it is not necessary forthis range to be made narrower for assembly purposes.

The Cp and Cpk values for this production run were 0.428 and 0.278 respectively givenour specifications and measured average critical dimension. For mass production, it isrecommended that these values be 1.33 at least, so these values are pretty low. We could increasethe tolerance range for the base part to increase these values. We could also modify processparameters and the mold to move the measured average closer to the middle of this tolerancerange.

5Coffee Top:

6 We were able to produce over 100 coffee top parts. The final parts produced weregenerally larger than the tolerance range of 2.310” - 0.005” for the diameter, averaging around2.316". Even though they were larger than our original intended specification, all of the partswere able to be used to assemble a complete yo-yo. The standard deviation for the coffee topproduction run was 0.00120”.

We introduced a disturbance in the process parameters during the production of parts 77

through 87. We decided to reduce the cooling time from 15 seconds to 1 second, producing apart that was 2.306, which is closer to and within our original intended specification. Thedisturbance is noticeable in both all charts, shown as a dip in the middle of the first and thirdgraphs on the page above as well as the lower bound outliers in the second graph. Reducing thecooling time is supposed to increase the shrinkage, as seen clearly in our example. This resultalso implies that we could have decreased our cooling time (though not to 1 second, as there issome warpage—dishing in the center of the part) slightly to bring our part closer to the range ofour original specification.

Our “rational subgroup” size is four. We chose this value because averaging thedimension of four parts gives a centralized measurement for the inner diameter and leaves uswith 36 averaged production runs. This gives us a good representation of the inner diameterdimension the process is producing, as well as enough data points to put in the Shewhart X-bargraph. The control limits were set three standard deviations above and below the measuredaverage, a range that enables us to see outlier average measurements and keep them from makingit through production. Three standard deviations also gives a sufficiently large range to accountfor the capabilities of the processes we use in manufacturing the yo-yo parts. Our parts were stillable to be assembled together and snap fit well even though the final parts were larger thanintended, and modifications can be made to adjust for these findings.

Our process capability, Cp, value was 0.696, and the Cpk was -2.135. Our Cp value isacceptable, as it only takes into account the tolerance range and the standard deviation, and canbe improved by increasing our tolerance from -0.005 to -0.010. On the other hand, the Cpk valuetakes into account the specified dimension, and since our final parts were larger than the originalintended specification, and thus is not only negative, but also almost two times the acceptablevalue of 1.33. Though currently not suited for mass production, we can increase our expecteddimension to 2.320" and change the tolerance to -0.010" to increase the Cp and Cpk values toabove the recommended value of 1.33.

7Coffee Foam:

8 We were able to produce over 100 coffee foam parts. All of the non-disturbance partswere produced within the tolerance range of 0.200” + 0.005”. The standard deviation for thecoffee top production run was 0.00215”.

We introduced a disturbance in the process parameters during the production of parts 61

through 71. For the parameter change, we decreased the forming time from 10 sec to 4 sec. Wecan see this change very clearly in the Shewhart X-bar chart as large peaks in the first and thirdgraphs, as well as the far right outliers in the second graph. Reducing the forming time causedsignificant warping in the middle of the coffee foam, increasing the height drastically. Thisresult implies that our forming time was fairly accurate for an efficient production run, asreducing the time had a large negative impact on the quality of the coffee foams.

We chose our “rational subgroup” size to be four. We chose this number becauseaveraging the dimension of four parts gives a centralized measurement for the height, and it stillleaves us with 27 averaged production runs. Altogether, this gives us a good representation of theheight dimension the process is producing, as well as give us plenty of data points to put in theShewhart X-bar graph. The control limits were also set three standard deviations above andbelow the measured average. This range was chosen because it enables us to notice outlieraverage measurements and keep them from making it through production. Three standarddeviations also gives a sufficiently large range to account for the capabilities of the processes weuse in manufacturing the yo-yo parts. Lastly, it is possible to still assemble our yo-yo using partswith critical dimension measurements within this range, so it is not necessary for this range to bemade narrower for assembly purposes.

The Cp and Cpk values for this production run were 0.777 and 0.729 respectively givenour specifications and measured average critical dimension. For mass production, it isrecommended that these values be 1.33 at least, so these values are low. We could increase thetolerance range to increase these values.

9Cup:

10 For our coffee cups, because the plastic is quite soft, measuring the diameter of our cupswas quite difficult. This resulted in some data that might not be as accurate. This factored intoour choice for subgroups. Since we had to make fewer cups (only 50 as opposed to 100), we hadto consider that we wanted enough data points to get a meaningful chart. At the same time,having too few samples in a subgroup could cause our measurement variability to show updisproportionately. Therefore, we decided that a subgroup of 4 would still work for this part. Thecontrol limits were set to be three standard deviations since that is a good way to see the processcapabilities. The cup process was relatively smooth and all of the measurements were withinspecification. These measurements were supported by the fact that all of the yo-yos fit perfectlyinto the cups.

For runs 31-40, we changed the heating time from 30 seconds to 15 seconds to simulate adisturbance. This drastically changed the appearance and functionality of the cup. With the lowerheating time, our cup could no longer sit flat on the table. This meant that it would fall over if theweight of the yo-yo was added. Also, all of the edges were more rounded and the part was lessdetailed. However, the critical dimension did not really change, as seen in our chart. This isbecause the heating time affects the sharpness of the features, but the only part that had a sharpfeature was the ledge. Our critical dimension was a flat side that was easily able to form anywaysdue to the number of vacuum holes. By decreasing the heating time, our part still formedcorrectly to our mold.

The standard deviation for the coffee top production run was 0.01411”. Our processcapability, Cp, value was 3.544, and the Cpk was 2.765. Our Cp and Cpk values are relatively high,indicating that most of the parts are within the specifications. Because on average, we hit thecritical dimension that is desired, but there is some slight variation, the Cpk value is lower thanthe Cp value. These high values indicate that we could probably go into mass production.Furthermore, we could probably lower our tolerances on these parts and still be fine.

During yoyo assembly, the biggest variability in assembly times was snapping the coffeeparts into the base, due to the necessity of both keeping the coffee top and foam aligned together,as well as holding them at the right angle before snapping them in. Winding the string also hadsome variability in assembly time because the string would sometimes keep slipping wheninitially winding. Since these two steps had the largest variabilities in assembly times, we wouldbalance the line by placing buffers after those two steps. That way, if those two steps weretaking longer than usual, the next step in line could continue assembling instead of waiting forthem to finish. We could also utilize more machines or workers to perform these steps. That wayyou could produce yo-yos at these stages twice as fast. This would reduce the need for buffersand balance out the production rate of each stage, bringing each one closer to 10 sec instead of15 or 20 sec.

12SECTION 4: Process AutomationSteps 3, part of step 4, 5 and 6 could be automated for high-volume assembly of our yoyo.

Step 3, inserting the set screw and spacer into the base parts, is repeatable and doesn’t require toomuch judgment or complex dexterity. A Delta robot with a three-finger gripper that rotatescould be used to perform both parts of this step.

Step 4 would be much more difficult to automate because the strings tend to get tangled, and itrequires dexterity to open the loop on the end of the string and put it on the yoyo. Twisting thebase parts together also requires caution in not pinching the string, although the twisting motionitself could be automated. A Delta robot with a vacuum suction gripper could pick up a basepart, center it with the other base part’s spacer, and rotate until the part screws into place.

Step 5, winding the string, would be more difficult to automate because the flexible nature of thestring makes it unpredictable. This step could potentially be automated if the string was clampedso that it was pulled taut enough to be straight, but loose enough to slide through the clamp as itwinds. A Delta robot could be used with a vacuum suction gripper to hold the base part and spinit quickly so that the string winds.

Step 6, placing the yoyo in the cup, would be easy to automate because it is just a pick-and-placeoperation. A Delta robot with a vacuum suction gripper could simply grip one face of the yoyo,and then center and lower it into the cup..

13SECTION 5: Specification Comparison

Part Parameter Expected Value Measured Value Tolerance

Base Inner Diameter 2.300” 2.302” +0.005”

Coffee Top Outer Diameter 2.310” 2.318” -0.005”

Coffee Foam Height 0.200” 0.200” ±0.005

Cup Inner Diameter 2.55” 2.58” ±0.15”

Differences in Expected and Measured Specifications

Base: We expected a shrinkage of 3% for the base, but in actuality there was almost noshrinkage due to the shim in our base part. We had to modify the mold before our production runin order to account for this lack of shrinkage. As a result, the part did not shrink all the way to2.300”. The measured dimension is still within the tolerance range, though, so we met thespecification.

Coffee Top: This was the one specification we did not meet. Although assembly still was not aproblem, this was still an unexpected outcome. We suspect that the plastic did not shrink asmuch as we thought it would. At the beginning of the year, we measured other parts similar tothis one and their molds. From these measurements we found that the part would likely undergoa 2% shrinkage in its outer diameter. It is possible that the cavities in the part prevented thecoffee top from shrinking radially, and thus, most of the shrinkage probably occurred in theheight dimension. If given the chance, we would change the specification to an expected value of2.320” with a tolerance of -0.010”.

Coffee Foam: We were able to meet this specification because the coffee foam’s height is notvery large. This means that relative to the height dimension, the tolerance of 0.005” is large.Also, due to the fact that the plastic sheet did not have to stretch as much, the coffee foam’sshrinkage is extremely small and the plastic does not want to unbend as much once it has beenformed. Not to mention that all of the bends in the plastic are small and close together. Thismakes these regions very stiff once formed. All of these factors help keep the manufacturedcoffee foam’s height dimension within the specified range.

Cup: Meeting the specification for the cup inner diameter was a fairly easy task. We made thetolerance for the cup inner diameter quite large. Perhaps it was too large, but we had designedthe die such that the plastic could not have a diameter of smaller than 2.55”. It was much morelikely that the plastic would unbend and make the inner diameter larger. As a result, we weremostly concerned with the inner diameter being too large even though this really is not a concernbecause we want the yo-yo to be easily placed inside and taken out of it. All in all, our largetolerance allowed for us to easily ensure that the specification was within the thermoformingprocesses capabilities.

14New Specification Chart for Mass Production:

Part Parameter Value Tolerance

Base Inner Diameter 2.300” + 0.010”

Coffee Top Outer Diameter 2.320” - 0.010”

Coffee Foam Height 0.200” ± 0.009”

Cup Inner Diameter 2.55” ± 0.10”

Base: We kept the expected dimension as 2.300” because it works for the assembly, but becausethe expected value for the coffee top’s outer diameter increased to 2.320”, we would need toincrease the tolerance to +0.010”. These specifications for the base and coffee top make sure thetwo can always press-fit together as long as the critical dimension is within the range. Thischange increases the Cp for the base to 0.856, but the Cpk does not change, as the averagedimension is closer to the LSL, which does not change. This may not be large enough for massproduction, but it is a significant improvement, and the Cp and Cpk could be improved even morewith slight changes to the mold.

Coffee Top: We increased the expected value of the outer diameter to 2.320”, so this way it iscloser to the measured average from our production runs. Similar to the base part, we then needto increase the tolerance change to -0.010” from -0.005” in order to ensure the two parts cansuccessfully press-fit as long as they are within the specifications. This change increases our Cpto 1.391 because we doubled the tolerance range. The Cpk only increases to 0.436 because themeasured average is close to one side of the new tolerance range. The Cp is large enough formass production, but the Cpk is not. This could be fixed by making changes to the mold to movethe average critical dimension away from the tolerance edge.

Coffee Foam: The coffee foam part does not need to be changed, as the measured average andstandard deviation were easily within specification. The Cp and Cpk for this process, though, wasnot greater than 1.33. If we increase the tolerance range to ±0.009”, the Cp and Cpk would thenbecome 1.398 and 1.350, and our part would be ready for mass production.

Cup: We decreased the tolerance range to ±0.10” because it is possible that not all cups in theold range of ±0.15” would work in the assembly. This still maintains the Cp and Cpk values above1.33 at 2.363 and 1.584, so the cup is still ready for mass production.

15SECTION 6: Mass ProductionAdditive Manufacturing Quotes – Shapeways

BaseThe material we chose for the base, out of those offered by the additive manufacturing siteShapeways, was the Blue Strong & Flexible Plastic. This meant that the process used tomanufacture the base would be Selective Laser Sintering (SLS). Other plastic materials offeredby Shapeways were HP Nylon Plastic, Frosted Detail Plastic, High Definition Acrylate, andPLA. Using HP Nylon Plastic or PLA would mean using a Multi Jet Fusion and FilamentDeposition Modeling method respectively. These are not desirable for our base because MJFleaves a slightly rough surface from the powder being fused together, while FDM leaves layerlines, especially for rounded parts. We would want the base, which fits into the hand during use,to be smooth for maximum comfort. The other materials were more expensive and given that thebase is not very detailed, would be unnecessary.

Number of Parts Cost Per Part Item Costs Additional Costs Total Cost

2 $11.47 $22.94 $4.99 (Shipping) $27.93

100 $11.47 $1147.00 $4.99 (Shipping) $1151.99

Coffee TopWe also chose the Strong & Flexible Plastic for the coffee top, this time in the orange color. Onelimitation of having the yo-yos printed from an AM service is that they do not offer all thecolors. Therefore, though we designed the part to be brown, we decided that orange would beclose enough, and if needed we could spray paint the parts afterwards. We chose the material forsimilar reasons as the base. In addition, the “flexible” aspect is important for this part since itmust snap into the base. There would be the possibility of the parts not fitting together with anyof the stronger plastics, as we saw when we initially prototyped our yo-yo design on the Form 23D printer.

Number of Parts Cost Per Part Item Costs Additional Costs Total Cost

2 $7.38 $14.76 $4.99 (Shipping) $19.75

100 $7.38 $738.00 $4.99 (Shipping) $742.99

Latte FoamThe White Strong & Flexible Plastic seemed like the best choice for the foam as well. Since thefoam has to fit into the coffee top perfectly, it seemed like it would be a good idea to 3D printthem using the same material and process (SLS). In our actual prototype yo-yo, we were able touse different processes (thermoforming and injection molding) because the materials used inthose processes generally have more flexibility than the materials used in additive manufacturingprocesses.

16 Number of Parts Cost Per Part Item Costs Additional Costs Total Cost

2 $4.89 $9.78 $4.99 (Shipping) $14.77

100 $4.89 $489.00 $4.99 (Shipping) $493.99

CupOnce again, the White Strong & Flexible Plastic was the best choice (an SLS process). While theother plastics would work for this part, as it does not need to be that flexible, they either do notcome in the right color and/or more expensive. PLA material would be the only other option thatcame in the right color and was not more expensive (it was the same price), but in that case itmakes more sense to use the SLS process which can have a thinner layer and allow for asmoother finish.

Number of Parts Cost Per Part Item Costs Additional Costs Total Cost

2 $11.76 $14.76 $4.99 (Shipping) $19.75

100 $11.76 $1176.00 $4.99 (Shipping) $742.99

Overall, there seems to be no difference in the cost per part in ordering higher volumes throughthe Shapeways service, and you only reduce cost because the shipping cost does not change.

17SECTION 7: Cost AnalysisIn order to perform the cost analysis, we used the following Excel spreadsheet . The costs arebroken down into material, tooling, equipment, and overhead. For each of the cases, we madesome assumptions as outlined below.

Case 1 – 2.008 Materials and Processes

Assumptions: ● We assumed that the resin for 3D printing the die was $150/liter, based on the range of prices from the Form Labs website. ● Based on the volume of each die from SolidWorks, we calculated the resin cost. Then, we added the 3D printing time multiplied by the given overhead time to calculate the overall tooling cost of the dies. ● Based on general estimates of mold life from online, we assumed that our molds would last 500,000 cycles before needing replacement. This is likely to be an overestimate. ● We did not include the cost of labor (the time we spent working on the manufacturing after design) in the overhead cost, which would have likely increased the per unit cost, instead considering it included in the overhead.

1819Case 2 – Additive Manufacturing Service

Assumptions: ● We assumed that the base would be redesigned so that it had threading where the nut would normally be, since we would not be able to 3D print with the nut embedded in. ● Since we would not be able to place the shim inside the base during production, we decided that the shims could be glued on during post-processing/assembly, which added an extra material. ● We set the volume limits to be 100,000 because that was when the unit cost was obviously leveling off and there were limits to the amount of parts that could be ordered on Shapeways. ● Due to constraints on the type of material and color available on Shapeways, we had to choose an orange color instead of brown for the coffee top.

2021Case 3 – High Volume Manufacturing

Assumptions: ● We decided that for effective high volume manufacturing, we would either have to buy machines that were capable of producing more parts in one cycle, or source the parts to a manufacturer capable of high volume manufacturing on non-dedicated machines. ● In the end, we decided to use the outside manufacturer for the estimate. ● We assumed that all of the parts would be injection molded instead of the 2 parts being thermoformed because the manufacturer we contacted said that our parts had features that were too narrow to quote in such high volume (This made sense since we 3D printed the die for thermoforming).

2223Comparison

Method # of Tooling Material Equipment Overhead Unit Cost

Units Cost/Unit Cost/Unit Cost/Unit Cost/Unit

2.008 50 $13.89 $2.39 $9.64 $37.23 $63.15

AM Service 50 - $1.58 $59.64* $9.39 $70.61

High Volume 100000 $0.05 $1.23 $12.01* $0.66 $13.95

Manufacturing (outsourced)*actually manufacturing cost - also includes parts of material and overhead cost

In our 2.008 manufacturing process, the overhead cost dominates. Much of this comesfrom the fact that the cost per hour of design labor is relatively high. Because of ourinexperience, we likely spent much more time on this than normal. At the same time, the per unitoverhead cost decreases with production volume - it is only at the low number of 50 that the highcost of the design labor is visible.

In the AM process, the manufacturing cost (the cost quoted by the service) dominates.This includes the material for 3D printing, the cost to run the printers, any post-processing costs,and any labor involved. The other costs (assembly materials and assembly) are insignificant incomparison, which we can see from the graph. This makes sense because the bulk of productionin this case is being done by the AM service.

Similarly, the manufacturing cost (quoted by ProtoLabs) is the dominant cost for highvolume manufacturing. This is because the contractor has to provide the material, equipment,and labor (which are included in this separate category because they are not broken down).Furthermore, the cost estimate provided by the manufacturer has to include some profit marginfor them. However, we can see that at a lower volume, the tooling cost is completely dominant asthe company has to create the new set of tooling for the custom parts. However, as theproduction volume increases, the tooling cost is still the same and the manufacturing cost (perpart) actually decreases.

Methods 1 and 3 are difficult to compare to method 2 because of the nature of theprocess. Overall, 3D printing all of the parts levels off at high production volume to a higher perunit cost than in any of the other methods. However, we can see that it is a good prototypingmethod because at low volume, the per unit cost is very similar. This is because with current 3Dprinting technology, the cost per part does not change as volume increases as it does withinjection molding. In fact, the only benefit you can get from producing more through an AMservice is that they charge a flat shipping rate for however many parts you order.

Our comparisons show that the per unit cost is the lowest at a high volume. Whenextending each of the processes to a high volume, we see that the leveled off unit cost is the

24lowest for the 2.008 process. However, this is not necessarily true in reality because we cannotassume perfect efficiency and in reality, all of us would likely be paid for the time we spentworking the machines etc. Thus, the comparison table that compares our unit costs at 50 yo-yosfor the first 2 methods and 100,000 yo-yos for the 3rd method likely shows the accurate pictureof when to choose each process for the lowest cost.

25Crossover Point Between Case 1 and Case 2

The unit cost of the yo-yo is lower when using an additive manufacturing service (+ somemanual assembly) until about 42 units, according to the analysis. At this point, the unit cost ofthe yo-yo through the additive manufacturing service levels off, while the unit cost of the yo-yowith our processes (injection molding and thermoforming) continues to decrease. The extremelyhigh tooling and overhead cost involved in the current process makes the additive manufacturingservice slightly cheaper when manufacturing at a low volume. However, since we needed tomanufacture a volume greater than this crossover point, the method we used is justified.Furthermore, due to our inexperience with mold making and general manufacturing, the toolingcosts are likely inflated, as we had to rework the molds many times.

26SECTION 8: Comparison with Store-Bought Yo-yo The sample yo-yo purchased from Amazon has a few differences from the ones wecreated. First of all, unlike our yo-yo, which can easily be unscrewed by twisting since we used aset screw, the sample yo-yo is tightly attached together and did not come apart even when wepulled and twisted it. On one hand, this is beneficial because the yo-yo is likely to break.However, because our yo-yo can unscrew, a worn string can be replaced or the string can bechanged out to suit people of different heights and preferences. Another difference is in the sizeand weight of the yo-yo. Our yo-yo is slightly larger (~0.2 in) in diameter than the sample one. Itcould be that the yo-yo manufacturers found the smaller size to be optimal for a younger market,which would make ours less desirable to very young children, but more desirable to an oldercrowd. Our yo-yo weighs slightly more because it contains 2 shims that are intended to increasethe weight and therefore, the performance and feel of the yo-yo. Upon comparing the ease ofusing each yo-yo, we concluded that the sample yo-yo was too light, making it slightly harder toyo-yo and not giving it the proper feeling in the hand.

Both yo-yos have some visible defects on them. The sample yo-yo looks like it is missinga chunk of plastic from the outside.

Our yo-yo is relatively unblemished, but since we did not post-process the bases, there isa small but noticeable bump from the gate on the side of each base. However, this would notlikely pose a problem, since the gate is visible on the sample yo-yo as well. The biggest flaw inour part would probably be the thermoformed latte foam. Since this part is relatively soft, itcould be destroyed if poked with a sharp object such as a pencil (though it will only deform, notfall out since it rests on a plastic part). This would only happen is someone intentionally wantedto destroy the yo-yo.

Even using the 2.008 processes (assuming the machines can run with high efficiency),according to the analysis, if we produce 5000 units, the yo-yo will be $12.34 each, which iscomparable to the yo-yos offered on Amazon, which range from $10-$15. However, it would notbe smart to sell them since the maximum profit margin we could get would be about 25%. Ofcourse, this price would be a lot lower if we were more experienced, as we would have fewerreworked molds and less time spent on designing (since we would be more familiar with thedesigning software). Using a high volume manufacturing process, the cost ends up being about$13.89 per yo-yo. This is higher than our estimate for the current process because for the currentprocess, we assumed as we scaled-up, there would be perfect efficiency, making the costestimate an underestimate. Given that we got the high volume manufacturing estimates as aquote from a manufacturer, they also had to include a profit margin for themselves, which wouldhave to be accounted for.

27 Even compared to the yo-yos sold on Amazon, the sample yo-yo we got was cheaper at$5. This is likely because it was entirely made of plastic. We had to include some metal partswhich increased the cost. Moreover, having it entirely out of plastic probably reduced assemblyrequired, which would decrease both the overhead cost and equipment cost (can run it onautomatic instead of semi-automatic). This reduced cost comes at the price of the quality of theyo-yo.